1. Field of the Invention
The present invention relates to a pressure sensor, a pressure sensor control apparatus, and a pressure sensor system which make it possible to perform automatic identification (automatic discrimination) of the type of the pressure sensor.
2. Description of the Related Art
Recently, the pressure sensor is widely used to measure the pressure of the pressure fluid or the like. Usually, the pressure sensor comprises a main pressure sensor body such as a semiconductor strain gauge, and an amplifier for outputting a voltage signal corresponding to a pressure applied to the main pressure sensor body. A casing of the pressure sensor is provided with DC (direct current) power source input terminals composed of two terminals for supplying the DC power source to the main pressure sensor body and to the amplifier, and a voltage signal output terminal for outputting the voltage signal corresponding to the applied pressure.
That is, the pressure sensor requires three input/output lines in total (three connecting terminals), i.e., two lines for supplying the DC power source and one line for outputting the voltage signal.
Conventionally, in order to identify the type of the pressure sensor, it is necessary to discriminate, by visual observation, the type name affixed to the pressure sensor by means of, for example, printing.
Practically, the voltage signal output of the pressure sensor is connected to a pressure sensor control apparatus. When the type is identified by means of the visual observation, it is necessary to perform the setting operation in order to allow the pressure sensor control apparatus to correspond to the type.
However, the pressure sensor itself is decreased in size in accordance with the recent advance to realize the small size and the light weight. It is difficult to easily identify the type name by means of the visual observation. Further, a problem arises such that it is also troublesome to perform the setting operation to allow the pressure sensor control apparatus to respond to the type of the pressure sensor. Further, in many cases, the pressure sensor is arranged at a position separated from the pressure sensor control apparatus to which the pressure sensor is connected. A problem also arises such that it is troublesome to identify the type name of the pressure sensor in such cases.
A pressure sensor has been suggested as a technique for solving the foregoing problems. That is, the pressure sensor is provided with a newly added terminal for outputting a type-identifying signal voltage for identifying the type. The input/output lines of the pressure sensor are composed of four lines in total (four connection terminals), i.e., two lines for supplying the DC power source, one line for outputting the voltage corresponding to the applied pressure, and one line for the terminal for outputting the type-identifying signal. In this arrangement, the type-identifying signal voltage is allowed to have a voltage value which differs depending on the type of the pressure sensor. Therefore, the type can be automatically identified by measuring the type-identifying signal voltage.
However, in the case of the pressure sensor having the four connection terminals, the input/output lines are four. Therefore, the production cost is increased corresponding thereto when the pressure sensor is produced. As a result, a problem arises such that the production cost is also increased when the pressure sensor control apparatus is produced.
Practically, a multi-conductor cable is frequently used for the input/output lines in some cases. However, in this case, a problem arises such that the cost of the four-conductor cable is more expensive than that of the three-conductor cable.
Another problem also arises such that when the input/output lines are four, the reliability of the signal connection is decreased as compared with the case in which the input/output lines are three.
The present invention has been made taking the foregoing problems into consideration, an object of which is to provide a pressure sensor, a pressure sensor control apparatus, and a pressure sensor system which make it possible to reliably identify the type even when the input/output lines are three.
According to the present invention, there is provided a pressure sensor comprising DC power source input terminals composed of two terminals, and a signal output terminal for outputting a signal corresponding to an applied pressure; the pressure sensor further comprising a power source current-setting means for allowing a power source current value flowing through the DC power source input terminals to be a power source current value which is different depending on a type of the pressure sensor.
According to the present invention, the power source current-setting means is used so that the power source current value flowing through the DC power source input terminals of the pressure sensor is allowed to be the power source current value which is different depending on the type of the pressure sensor. Accordingly, it is possible to obtain the pressure sensor in which the type can be identified while maintaining the three input/output lines, by detecting the power source current value.
According to another aspect of the present invention, there is provided a pressure sensor control apparatus to be connected with DC power source input terminals composed of two terminals, and a signal output terminal for outputting a signal corresponding to an applied pressure, of a pressure sensor, for performing predetermined process in accordance with the signal output; the pressure sensor control apparatus comprising a power source current value-detecting means for detecting a power source current value flowing through the DC power source input terminals; and a type-identifying means for identifying a type of the pressure sensor in accordance with the detected power source current value.
According to the present invention, the power source current value, which is supplied to the pressure sensor and which is allowed to flow through the DC power source input terminals, is detected by the power source current value-detecting means. Therefore, the type of the pressure sensor can be identified by means of the type-identifying means on the basis of the detected power source current value.
Since the power source current value is detected, the pressure sensor control apparatus capable of identifying the type can be obtained, while maintaining the three input/output lines for the pressure sensor.
In this arrangement, the pressure sensor control apparatus is constructed to include a plurality of connection terminals which make it possible to simultaneously connect a plurality of pressure sensors having different power source current values. Accordingly, it is possible to simultaneously identify the types of the plurality of pressure sensors by using one pressure sensor control apparatus.
According to still another aspect of the present invention, there is provided a pressure sensor system comprising pressure sensors set to have power source current values which are different from each other depending on types; and a pressure sensor control apparatus including a type-identifying means to which the pressure sensors are connected, for detecting the power source current value to identify the type of the pressure sensor when predetermined process is performed in accordance with an output of the pressure sensor.
According to the present invention, it is possible to construct the pressure sensor system in which each of the pressure sensors and the pressure sensor control apparatus are connected to one another by using three lines.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.